When disposable absorbent articles are concerned, previously large efforts have been made in order to obtain good properties for absorption of exudated body fluids. For this reason, on their front sides, absorbent articles of the type in question are provided with special liquid-pervious front side layers, which are designed for a rapid liquid acquisition and for providing a dry surface on the side of the article which faces towards a user also after repeated absorptions of body fluids. Normally, this effect is achieved by means of providing suitably designed openings for liquid acquisition through the front side material, and by means of selecting polymer materials in the front side material which not easily absorb exudated body fluids, but instead let the body fluids pass through to underlying layers in the absorbent structure.
On their backside, absorbent articles of the type in question usually are provided with a liquid-impervious backside material, which prevents exudated body fluids from striking through and soiling the clothing of the user.
Conventional front side and backside materials of absorbent articles usually comprise nonwoven or film materials of synthetic polymers, which normally are based on crude oil and are not biologically degradable in the short term.
Since landfill and sometimes composting is utilised in order to dispose of disposable absorbent articles after use, previously attempts have been made to find replacement materials, which are biologically degradable in the short term, for the synthetic polymers which normally are included in the front side and backside materials of absorbent structures and articles.
Accordingly, the international patent application nr. PCT/US90/07169 discloses disposable absorbent structures and absorbent articles in which the front side and/or backside material comprise(s) a polyester which is based on lactic acid or glycolic acid. The utilised polyesters are said to be designed for being degradable by means of a simple hydrolysis, for example in landfill.
Furthermore, the Japanese patent application JP 93-022109 discloses a biologically degradable, thermoplastic polymer with a higher melting point than 100° C. It is stated that the polymer preferably comprises poly-3-hydroxy-propionate (or -butylate, -capreolate, -heptanoate or -octanoate) and copolymers thereof, poly-gamma-butyrolactone, polyethylene succinate, polybutylene succinate, polyneopentyl succinate (or -oxalate), polyglycolide, polylactide and copolymers or mixtures thereof. Staple fibres of the biologically degradable polymer are claimed to be useful in surface materials for disposable diapers or sanitary napkins, or in other materials for hygiene use. The biologically degradable staple fibre disclosed in JP 93-022109 is claimed to be resistant to higher temperatures than 80° C., hydrophobic, heat-fusible, and completely biologically degradable after use by means of environmental influence.
As has become evident from the foregoing, an absorbent article, for example a diaper or a pair of training pants for infants or incontinent adults, an incontinence guard, a sanitary napkin, a pantyliner, or the like, usually comprises a liquid-pervious cover layer on the side of the article which is intended to face towards a user when the article is used. On the side of the article which is intended to face away from the user when the article is used, the absorbent article is provided with a liquid-impervious cover layer, wherein the liquid-pervious cover layer and the liquid-impervious cover layer together enclose an absorbent structure. The absorbent structure comprises an absorbent core, which usually consists of cellulose fluff pulp with an addition of highly absorbent polymer, so-called superabsorbent.
Between the absorbent core and the liquid-pervious cover layer, a liquid-acquiring layer, which can consist of a porous, open wadding structure with high wettability, is usually provided. In order to obtain a rapid liquid acquisition and a high surface dryness of the liquid-pervious cover layer on the outside, it is important that the liquid-acquiring layer exhibits a high hydrophilicity and, consequently, a low contact angle to the liquid which is to be absorbed. A high hydrophilicity can be obtained by means of manufacturing the liquid-acquiring layer from hydrophilic fibres, for example viscose fibres or lyocell fibres. Since structures with such regenerated cellulosic fibres have a tendency to collapse when wetted, fibres based on synthetic polymers are often utilised or mixed into the liquid-acquiring layer, in spite ot the fact that such synthetic fibres exhibit a high intrinsic hydrophobicity which actually is undesired for a liquid-acquiring layer.
In order to improve the wettability, i.e. increase the hydrophilicity, of liquid-acquiring layers which comprise conventional synthetic fibres, the synthetic fibres or the entire liquid-acquiring layer is usually treated with a suitable surfactant. A disadvantage which can occur as a consequence of such surfactant treatment is that certain surfactants, particularly at high addition levels, may give sensitive users skin irritations. Another previously known problem with such surfactant treatment is that the wettability is impaired after repeated wettings with body fluid, i.e that the hydrophilicity obtained by means of the surfactant treatment is non-permanent.
In order to obtain maximum liquid transport between the different material layers in the material structure of an absorbent article, the material layers should be brought into closest possible contact with each other. Thereby, the use of an adhesive for binding the material layers can result in an impaired wettability, since the type of adhesive s in question usually are of a hydrophobic nature. For this reason, thermobonding of thermoplastic fibres included in the material layers is preferred instead of adhesive bonding. Something which can be perceived as a disadvantage with thermobonding of conventional synthetic fibres is that the included polymers require a relatively high temperature, usually considerably higher than 100° C., in order to be possible to bind thermally. When manufacturing material structures for absorbent articles, such high temperatures can be difficult to achieve without impairing for example the wettability of the cellulosic fibres included in an absorbent core.
As has become evident from the foregoing, another disadvantage with conventional synthetic fibres is that they are not biologically degradable in the short term and, furthermore, are based on raw materials which are non-renewable in the short term.